Roll or buffer stores for flat web materials, particularly for web-shaped packaging materials or films, are known and are used in systems for processing the flat material, for example in packaging systems, to maintain a predetermined web tension by intermediate storage of a variable length of the flat material. Buffer stores of this type comprise at least two roller registers. These roller registers have parallel rollers that are spaced apart from one another. These rollers are mounted so as to freely rotate in the roller registers. As it is guided over these rollers, the flat web forms a plurality of loops.
The roller registers are arranged to be movable relative to one another. In some cases, one roller register is fixed and the other roller register is movable, for example, by being pivotable in an axis direction radially to the rotation axis of the rollers.
A spring causes tension in the flat material between the roller registers. In known buffer stores, this spring is formed by at least one piston-cylinder arrangement, such as a pneumatic cylinder. This cylinder has at least one cylinder chamber to which the operating pressure of a compressible fluid can be applied. A suitable compressible fluid is air. The piston-cylinder arrangement thus acts as a gas spring or as a compressed-air spring.
A disadvantage of these known buffer stores is that, in the event of a fault, and particularly if the flat web material tears, the full working pressure still acts in the cylinder chamber. As a result of this tear, the now-torn flat material can no longer hold the movable roller register back. As a result, the roller register suddenly moves to the end position of its movement stroke or pivot stroke. This sudden and violent movement of a heavy object causes a significant risk of injury to operating personnel.